ABSTRACT
Electron energy loss spectroscopy (EELS) is a technique with the ability to probe the electrical activity of extended defects in semiconductors. In a cold field emission gun scanning transmission electron microscope under carefully chosen experimental conditions it is possible to detect states due to the extended defects in wide band gap materials and these can be compared directly with density functional theory calculations of the energy loss. Density functional theory calculations predict energy levels localised on the dislocation cores for the edge as well as for the screw dislocations in gallium nitride (GaN) that should show in low EEL measurements as a supplementary absorption below the bulk band edge. Thicker lines represent the step function-like bulk spectra, with steepest rise at the bandgap energy. The atomic structure of dislocations, particularly in functional materials, for example, GaN, remains of great interest and is controversial.
